Adipose tissues secrete a variety of signaling molecules that regulate systemic glucose and lipid metabolism. Leptin, which was discovered in 1994, is a primary adipose hormone that conveys an adiposity signal to the brain. The brain, particularly the hypothalamus, integrates leptin and various other metabolic signals to regulate energy homeostasis and body weight by controlling both behavior and metabolic responses. Leptin decreases body weight both by suppressing appetite and by increasing energy expenditure.
Obesity represents a risk factor for many diseases such as colon cancer, hyperlipidemia, hypertension, arteriosclerosis, and diabetes. No method for treating or preventing obesity with a medicine has been established. On the basis of the recent findings about leptin, treatment of obesity by administering leptin was attempted but ended in failure. This may be caused by “leptin resistance”, which means decreased response to leptin, developed in patients of obesity. Leptin resistance likely results from the impairment in leptin transport to the brain, leptin signaling, and/or the neurocircuitry in the hypothalamus that regulate energy homeostasis, but the mechanism causing leptin resistance has not been completely revealed.